During the fifth year of the multiple sclerosis we will continue to follow-up the cohort of individuals with multiple sclerosis on April 1, 1970, in the King-Pierce County areas of Washington State and Los Angeles County, California. Analysis will be carried out on the follow-up conducted in the fourth year of the study. Enrollment of the patients with an acute exacerbating course of multiple sclerosis and their co-habitant controls will be completed. Preliminary analysis will begin on possible relationships between immune responses to selected viral and brain antigens, clinical course, and genetic tissue types. The genealogies of families with multiple cases of multiple sclerosis will be completed, diagnoses of living cases verified, and the patients and their faimilies interviewed. The case-control study, using childhood playmates as controls and mothers of both the cases and controls as additional informants, will begin during the fifth year of the study. Investigation of an apparent time-space cluster of cases occurring among students attending a particular high school in King County in 1954-55 will continue by identifying additional cases from responses to a tabloid questionnaire sent to all students in attendance at that time. A case-control study, using cases and controls from the study school, will be continued; and, in addition, environmental and demographic characteristics of the study will be compared with a school reporting fewer than the expected number of cases. BIBLIOGRAPHIC REFERENCE: R. Detels, B. Visscher, A. Coulson, R. Malmgren and J. Dudley.: Multiple Sclerosis in Japanese-Americans--A Preliminary Report. International Journal of Epidemiology, Vol. 3, No. 4, pp. 341-345, 1974.